Numbers 35:9-13

And the LORD spake unto Moses, saying,

Speak unto the children of Israel, and say unto them, When ye be come over Jordan into the land of Canaan;

Then ye shall appoint you cities to be cities of refuge for you; that the slayer may flee thither, which killeth any person at unawares.

And they shall be unto you cities for refuge from the avenger; that the manslayer die not, until he stand before the congregation in judgment.

And of these cities which ye shall give six cities shall ye have for refuge.